Current methods of measuring and observing drilling parameters in an oil and gas well system during a drilling operation, such as drill string weight, torque, vibration, speed of rotation and internal pressure are generally indirect, meaning that they are measured at a point conveniently accessible but not necessarily located on the actual drill sting.
For example, the drill string weight is often indirectly measured by measuring the pull on a cable of a hoisting system, which raises and lowers the drill string. This type of measurement is inaccurate due to frictional forces associated with the cable, the sheaves, and the measurement device attached to the cable.
The drill string torque is difficult to measure since it is often difficult to measure the torque output of the torque driving system, which rotates or drives the drill string. For example, typically, the drill string is either rotated with a large mechanical drive called a rotary table or directly by a large motor called a top drive. The torque output of each of these drive systems cannot be easily measured and most often is either calculated from the current going to the drive motor when a top drive is used, or by measuring the tension of a drive chain which drives the rotary table when a rotary table is used. Both of these methods are very inaccurate and subject to outside influences that can cause the readings to be inconsistent, such as stray electrical currents through the drive motor when a top drive is used, or wear of the measured mechanical devices when a rotary table is used.
Another drilling parameter that is difficult to measure is vibration. Vibration of the drill string is very damaging to its components especially to the drill bit at the end of the drill string, which drills a well bore.
Various methods have been proposed to solve the above described problems with the measuring of drilling parameters during a drilling operation, including installing various instrumented pins onto components of the hoisting system or the torque drive system. Other more direct approaches have been tried with limited success. For example, some have installed a load sensor at the top of the derrick for measuring pull of the hoisting system on the derrick. These are commonly referred to as crown block weight sensors.
Various other devices have been developed for directly measuring torque and vibration on the drill string. For example, one such device for use with a rotary table includes a plate that attaches to the top of the rotary table between the table and a drive bushing, referred to as the kelly drive bushing. However, currently more and more oil and gas well drilling systems are using top drive drilling systems instead of rotary tables, rending this approach less desirable and possibly obsolete.
Others have tried to make special instrumented subs that screw directly into the drill string. One such device is large and bulky and does not fit into existing top drive systems. These devices provide the accuracy desired in the measure of the drilling parameters, but compromise the drilling equipment due to their size and shape. In addition, these devices require redesign of the torque drive system to accommodate them.
Accordingly, a need exists for an apparatus and method for accurately measuring drilling parameters during a drilling operation that does not require modification of the torque drive system to which it attaches.